I have looked and I have found multiple posts. I am not afraid to fix my car but I am hoping that you nice folks will help me once and for all with some troubleshooting.....

My car has eaten up many coils. They are easy to replace and I assumed that after 240,000 miles I should expect a few to burn out. Sound about right?

But I am also getting those codes... P0171 and P0174, lean bank 1 and 2. Are they related? I dont think so. A friend of mine owns a NAPA and subscribes to a service called "Service Repair Solutions, Inc." ... here is what that service said regarding those codes:

Engine Control Module (ECM) receives information from the heated oxygen sensor about fuel/air mixture in different load areas. If ECM registers that fuel/air mixture deviates too much from the targat lambda, so that adaptations from Bank 1 end up in any of its end-positions, the diagnostic trouble code is generated.

Possible Source

Too high ethanol content in fuel

Incorrectly installed/damaged oil dipstick (air leakage)

Damaged or Incorrect type of injector values

Air leakage, exhaust pipe

Low fuel pressure

Damaged mass air flow sensor

Fault Symptom

Malfunction indicator lamp (MIL) lit

Poor performance

Engine misfires

High idle rmp

So, I am getting the misfires but after replacing a coil the CEL does not go away, even after I clear the code.

Some looking around produced the possibility that it was maybe the PCV oil trap cover. I do hear a hum but when I place a latex glove over the oil filler there is negative crankcase pressure (the glove does not blow up... actually wants to suck in) which is good?

What else do people suggest??? I don't want to go replacing expensive parts.

People should note this trouble pertains to the 3.2l 6 cyl. engine. It's a 2008 VC-70, no?
1) The location of the IAC valve would be helpful. I know they break on Ford engines so maybe cleaning/changing is in order.
2) Always inspect for split incoming air handling hoses and vacuum leaks (as mentioned).
3) The MAF sensor was mentioned in your "NAPA service" sourced diagnosis so inspect and clean it with MAF cleaner ONLY.
4) Switch to a premium fuel which has no ethanol. Sunoco and others' premium are ethanol free.
5) How many miles on this car? O2 sensors do die.
6) A real VIDA readout at a dealer or adequately equipped indie might be the smartest next step. Blindly throwing parts at an unknown problem is expensive.

Also, I have no rational for any car eating spark coils except incorrect plugs. Are your sparky-poos that right ones?

Regarding the dipstick seal: Is it intact? It's a soft "O" ring.

Regarding "Damaged or incorrect type of injector values": Was the car "E-Tuned" or "Chipped" or otherwise monkeyed with in its previous life?

Check the exhaust manifold and exhaust pipe where a sensor may have been removed and where damage may have resulted. Look for amateurish repairs.

No IAC valves after 2000 except the s40/v40 4 cylinder 200-2004.
Both banks having lean code is unlikely two bad O2 sensors.
Air leaks need to be looked for. MAF sensor could be the cause.
The breather is OK. Flow vacuum is normal, if the diaphragm ruptures it gets high vacuum and would have sucked the glove down into the filler cap hole.
Exhaust leaks can make the O2 sensors show lean, IS the MPG poor on this car?

How does it run?
The fuel pressure sensor could be faulty and the fuel pressure reported and controlled is actually low and the ECM is richening up mixture to cover and sets code when the adjustment amount reaches the acceptable limit.

These 6 cylinders have few coil issues so that is odd. What do the plugs look like? Are the gaps really wide when the coils fail?

Car is a '08 XC70 with the 3.2 v6. 240,000 miles with no monkeying around... no modifications.

fuel mileage is poor

the glove did want to get sucked in pretty good

haven't changed plugs lately, I'll take a look today

I've never replaced the MAF but will pull it and clean it

I'm guilty of using mid-grade fuel... will put super in

what "breather" are you referring to? the PCV oil trap?

I sprayed around the engine compartment looking for vacuum leaks. I'll pull the air box and do a closer inspection

O2s do die... I just want to exhaust my options before I throw some $ at those

I want to also mention that the READ drive is gone or going. My mechanic has never replaced a READ but talking to the dealership they purchase parts from he was told that every time a READ has been repaired (by the dealership), the repair has had problems. It's an expensive repair requiring special tools. Problem is, I need an inspection sticker so I need this CEL to go away.

At that mileage you should have all new coils and plugs every 50k miles or so.

Your lean run condition can be diagnosed by looking at the fuel trim at idle and at 2500 rpm,to see if the air leakage or fuel delivery is the culprit. You do need some tools to measure this that cost $100-200 or pay the man.

Lean running can cause hot top engine end. It can damage the ignition coils. Maybe keep the engine cover removed. The thermostat can also fail closed and cause overheating on the 3.2 Worn spark plugs can also damage the coils. Are you using genuine coils?